JP4065213B2 - Silicon substrate etching method and etching apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a silicon substrate etching method and an etching apparatus for forming a structure surface such as a groove on a silicon substrate by a dry etching process.
[0002]
[Prior art and problems to be solved by the invention]
A structure such as a groove is formed on a silicon substrate by a dry etching process. For example, in the field of semiconductor integrated circuits, higher integration and higher density are being promoted, and trenches (deep grooves or deep holes) are formed with high precision. There is a need for an etching technique that can be formed. As an etching method for the purpose of such trench etching, an etching method as disclosed in Japanese Patent Publication No. 7-503815 is conventionally known.
[0003]
In this etching method, after an etching mask having a desired shape is formed on the surface of a silicon substrate, SF is converted into plasma. ₆ Etching process that forms a groove or a hole by dry etching the substrate surface using a mixed gas of Ar and Ar, and CHF that has been converted to plasma ₃ And a mixed gas of Ar and a polymerization process (protective film forming process) in which a protective film is formed on the side wall of the groove or hole (hereinafter referred to as a groove or the like) alternately. A deep groove or the like).
[0004]
According to this etching method, the wall surfaces of grooves and the like sequentially formed by dry etching are then covered with a protective film, and the wall surfaces are protected by this protective film during subsequent dry etching. Undercut is prevented, and a groove or the like having an apparently vertical wall surface can be formed.
[0005]
However, the etching method described above has the following problems. That is, the etching method described above is an etching process that does not involve the formation of a protective film on the wall surface and a process of forming a protective film on the wall surface, which are alternately repeated. The wall surface is in a state where a protective film is not formed. For this reason, in the etching process, this wall surface is etched together with the etching ground (bottom surface of the groove or the like), and as a result, the wall surface is wavy in the vertical direction, resulting in poor processing accuracy. Then, due to such unevenness formed on the wall surface, high integration and high density in the field of semiconductor integrated circuits have been hindered.
[0006]
Therefore, the inventors of the present invention have both the etching process and the protective film forming process using a mixed gas of an etching gas and a protective film forming gas in a state where a bias potential is applied by constantly applying electric power to the silicon substrate. In the etching process, a mixed gas of a large amount of etching gas and a small amount of protective film forming gas is used, and in the protective film forming step, a mixed gas of a small amount of etching gas and a large amount of protective film forming gas is used. An etching method has already been proposed in Japanese Patent Application No. 2001-299435.
[0007]
According to this etching method, the etching process and the protective film forming process are performed using a mixed gas of an etching gas and a protective film forming gas. Therefore, in the etching process, the etching ground is etched by the etching gas and etching is performed. The vertical structure surface sequentially formed by the step is immediately covered by the protective film formed from the protective film forming gas, and in the subsequent protective film forming step, the vertical structural surface is more firmly covered by the protective film. The Thereby, the etching with respect to the said vertical structure surface is suppressed, the unevenness | corrugation of the surface is small, and also the perpendicular structure surface excellent in the perpendicularity can be formed.
[0008]
In addition, since a bias potential is applied by constantly applying power to the silicon substrate, the etching ground can be physically etched by ion irradiation, and the etching speed is increased in the etching process, while the etching ground is formed in the protective film forming process. Further, it is possible to prevent the protective film from being formed, and as a result, the entire etching processing time can be shortened.
[0009]
However, in this etching method, as described above, the etching is performed using the mixed gas of the etching gas and the protective film forming gas, so that the vertical structure surface formed by the etching can be effectively protected. On the other hand, in the etching ground, etching by etching gas or ion irradiation and the conflicting action of forming a protective film that suppresses this etching proceed simultaneously, so that the energy that makes the etching action is also spent on the peeling of the protective film. Therefore, this method has a demerit that the etching rate is reduced as compared with an etching method that does not use a protective film forming gas during etching.
[0010]
In addition, the protective film forming step can suppress the formation of the protective film on the etching ground by the etching gas or ions, and has the effect of shortening the entire etching processing time. Since the etching gas also acts on the vertical structure surface, it becomes an environment where the vertical structure surface is easily etched, and in some cases, there is a demerit that the surface cannot be sufficiently smoothed.
[0011]
Therefore, as a result of intensive research on the mixing ratio of the mixed gas, the inventors have not used a protective film forming gas in the etching progress process, and compared with an etching method that does not use an etching gas in the protective film forming process. The inventors have obtained knowledge about the optimal mixing ratio that increases the etching rate and that the vertical structure surface formed by etching is sufficiently smooth and has excellent perpendicularity.
[0012]
Thus, the present invention provides an etching method and etching apparatus for a silicon substrate capable of making the vertical structure surface formed by etching sufficiently smooth and excellent in perpendicularity without reducing the etching rate. For the purpose of provision.
[0013]
[Means for solving the problems and effects thereof]
In order to achieve the above object, the present invention provides a mask forming process for forming an etching mask on a silicon substrate surface, and dry etching the silicon substrate surface from an opening of the etching mask using an etching gas that has been made plasma by high-frequency power. And etching the silicon substrate by sequentially performing an etching process for forming a predetermined structural surface,
The etching step,
While constantly applying power to the silicon substrate to give a bias potential,
SF as etching gas ₆ Gas and C as protective film forming gas ₄ F ₈ Using a mixed gas with a fluorocarbon gas (CxFy) such as the above, mainly to advance the dry etching in an etching ground;
Same SF ₆ In the etching method in which a mixed gas of a gas and a fluorocarbon gas is used to sequentially repeat a step of forming a protective film mainly on the structural surface perpendicular to the etching ground.
The mixed gas in the dry etching process is changed to SF. ₆ It is assumed that 5 to 12 volumes of fluorocarbon gas are mixed with 100 volumes of gas,
The mixed gas in the protective film forming step is SF with respect to 100 volumes of fluorocarbon gas. ₆ The present invention relates to a method for etching a silicon substrate, wherein 2 to 5 volumes of gas are mixed.
[0014]
According to this invention, in the step of proceeding with the dry etching, the etching ground is SF. ₆ Etching is performed by gas or ion irradiation, and a vertical structure surface sequentially formed by etching is immediately covered with a protective film derived from fluorocarbon gas.
[0015]
In the subsequent protective film forming step, the vertical structure surface is more firmly covered with the protective film, and the formation of the protective film on the etching ground due to etching gas or ion irradiation is suppressed. The
[0016]
As described above, the mixed gas in the dry etching process is SF. ₆ A mixture of 5 to 12 volumes of fluorocarbon gas per 100 volumes of gas, ie SF ₆ What mixed gas and fluorocarbon gas in the range of 100: 5-12 by volume ratio is preferable. If the amount of the fluorocarbon gas is less than 5 volumes, the amount of the fluorocarbon gas is too small to effectively protect the vertical structure surface formed by etching, while the amount of the fluorocarbon gas exceeds 12 volumes. In addition, the amount of fluorocarbon gas is so large that a protective film is easily formed on the etching ground, and the energy for performing the etching action is spent on the peeling of the protective film, and the etching method does not use the protective film forming gas at the time of etching. This is because the etching rate is lower than that.
[0017]
Further, the mixed gas in the protective film forming step is SF with respect to 100 volumes of fluorocarbon gas. ₆ Gas mixed with 2 to 5 volumes, that is, fluorocarbon gas and SF ₆ What mixed gas in the range of 100: 2-5 by volume ratio is preferable. SF ₆ If the amount of gas is less than 2 volumes, SF ₆ Since the amount of gas is too small to sufficiently suppress the formation of a protective film on the etching ground, a sufficient etching rate cannot be obtained. ₆ If the amount of gas exceeds 5 volumes, SF ₆ This is because the amount of gas is so large that the vertical structure surface is easily etched and the surface accuracy is deteriorated.
[0018]
Thus, according to this invention, SF ₆ A mixed gas of gas and fluorocarbon gas is used, and the mixed gas in the dry etching progressing process and the mixed gas in the protective film forming process are set to the above-mentioned mixing ratio, so that the protective film forming gas is changed in the dry etching progressing process. Compared to an etching method that does not use and does not use an etching gas in the protective film formation step, the etching rate can be increased, and the vertical structure surface formed by etching can be a smooth surface with high surface accuracy.
[0019]
Further, it is preferable that the power applied to the silicon substrate is increased in the dry etching progressing process and is decreased in the protective film forming process. In this way, the irradiation rate of ions in the dry etching progressing step can be increased and the etching rate can be increased. On the other hand, in the protective film forming step, the protective film formed on the vertical structure surface is peeled off by irradiation ions. It is possible to prevent the vertical structural surface from being effectively protected.
[0020]
Furthermore, it is preferable that the high-frequency power for generating the plasma is increased in the dry etching progress process and decreased in the protective film formation process. In this way, in the dry etching process, SF is used. ₆ The gas is efficiently turned into plasma and the etching rate is increased. On the other hand, SF is formed into plasma in the protective film formation process. ₆ The ratio of the gas is reduced, and the vertical structure surface is hardly etched, and the vertical structure surface can be more effectively protected.
[0021]
The etching process may be started from a dry etching progress process or a protective film forming process. However, starting from the protective film forming process makes the unevenness of the vertical structure surface smaller. It is preferable in that it can be performed.
[0022]
And the etching method mentioned above can implement this suitably with the following etching apparatuses.
[0023]
That is, the etching apparatus includes an etching chamber for storing a silicon substrate to be etched, a base disposed at a lower position in the etching chamber, on which the silicon substrate is placed, and etching in the etching chamber. SF which is gas ₆ An etching gas supply means for supplying a gas; a protective film forming gas supply means for supplying a fluorocarbon gas as a protective film forming gas into the etching chamber; a decompression means for reducing the pressure in the etching chamber; and an outer periphery of the etching chamber. The SF provided to the etching chamber is provided with a coil disposed so as to face the coil, and high-frequency power is applied to the coil. ₆ Plasma generating means for converting gas and fluorocarbon gas into plasma, base power applying means for applying high frequency power to the base, etching gas supply means and protective film forming gas supply means are supplied into the etching chamber. The SF ₆ Gas flow control means for controlling the flow rate of gas and fluorocarbon gas, coil power control means for controlling power applied to the coil of the plasma generation means, and power applied to the base by the base power application means And a base power control means for controlling
The gas flow rate control means is the SF ₆ Gas and fluorocarbon gas are supplied into the etching chamber continuously and the supply amount is periodically changed, and the supply amount is controlled so that the phases of both are reversed, and the SF is further provided. ₆ SF when supplying a large amount of gas ₆ 5 to 12 volumes of fluorocarbon gas are supplied to 100 volumes of gas, and SF is supplied to 100 volumes of fluorocarbon gas when supplying a large amount of the fluorocarbon gas. ₆ It is configured to supply 2 to 5 volumes of gas.
[0024]
The base power control means converts the power applied to the base to the SF. ₆ It is preferable that the flow rate is increased when supplying a large amount of gas, and is decreased when supplying a large amount of the fluorocarbon gas.
[0025]
Similarly, the coil power control means converts the power applied to the coil to the SF. ₆ It is preferable that the flow rate is increased when supplying a large amount of gas, and is decreased when supplying a large amount of the fluorocarbon gas.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings.
[0027]
First, the configuration of the etching apparatus according to the present embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view partially showing a schematic configuration of an etching apparatus according to the present embodiment.
[0028]
As shown in FIG. 1, this etching apparatus 1 is made of a ceramic or the like, and is provided in a housing-like etching chamber 2 in which an etching chamber 2a is formed, and a lower region in the etching chamber 2a. The base 3 on which the silicon substrate S as an etching material is placed, and the SF as an etching gas in the etching chamber 2a ₆ Gas and protective film forming gas C ₄ F ₈ A gas supply unit 7 for supplying fluorocarbon gas (CxFy) such as, a decompression unit 13 for decompressing the etching chamber 2a, and SF supplied into the etching chamber 2a ₆ A plasma generation unit 15 that converts gas and fluorocarbon gas into plasma, a high-frequency power source 18 that applies high-frequency power to the base 3, and a control device 20 that controls the operation of these units are provided.
[0029]
On the base 3, the silicon substrate S is placed via a seal member such as an O-ring 4. The base 3 is provided such that the base 3a is led out of the etching chamber 2a, and a communication path 5 leading to a space 5a formed between the base 3 and the silicon substrate S is provided at the center thereof. The space 5a is filled and sealed with helium gas through the communication path 5. In addition, a cooling water circulation path 6 is formed in the base 3, and the silicon substrate S is formed via the base 3 and helium gas by cooling water (20 ° C.) circulating in the cooling water circulation path 6. It is designed to be cooled. Further, a high frequency power of 13.56 MHz is applied to the base 3 by the high frequency power source 18, and a bias potential is generated in the base 3 and the silicon substrate S placed on the base 3. Yes.
[0030]
The gas supply unit 7 includes a gas supply pipe 8 connected to the upper end of the etching chamber 2 and gas cylinders 9 and 10 connected to the gas supply pipe 8 via mass flow controllers 11 and 12, respectively. A gas whose flow rate is adjusted by the mass flow controllers 11 and 12 is supplied from the gas cylinders 9 and 10 into the etching chamber 2a. In this example, the gas cylinder 9 contains SF for etching. ₆ The gas cylinder 10 is filled with gas, and the protective film forming C ₄ F ₈ Filled with gas.
[0031]
The decompression unit 13 includes an exhaust pipe 14 connected to the lower end of the etching chamber 2 and a vacuum pump (not shown) connected to the exhaust pipe 14, and the etching chamber is configured by the vacuum pump (not shown). The inside of 2a is depressurized to a predetermined low pressure.
[0032]
The plasma generation unit 15 includes a coil 16 disposed along an outer periphery at a position higher than the base 3 of the etching chamber 2, and a high frequency power source 17 that applies high frequency power of 13.56 MHz to the coil 16. Thus, by applying a high frequency power to the coil 16, a varying magnetic field is formed in the space in the etching chamber 2a, and the gas supplied into the etching chamber 2a is turned into plasma by the electric field induced by this varying magnetic field. It has become.
[0033]
The controller 20 is applied to the coil 16 and the gas flow control means 21 for controlling the mass flow controllers 11 and 12 to adjust the flow rate of the gas supplied from the gas cylinders 9 and 10 into the etching chamber 2a. It comprises coil power control means 22 for controlling high-frequency power and base power control means 23 for controlling high-frequency power applied to the base 3.
[0034]
Next, the aspect which etches the silicon substrate S with the etching apparatus 1 provided with the above structure is demonstrated.
[0035]
First, an etching mask having a desired shape using photolithography or the like (for example, a resist film or SiO 2 ₂ After the film is formed on the silicon substrate S, the silicon substrate S is loaded into the etching chamber 2 and placed on the base 3 via the O-ring 4. Thereafter, helium gas is filled and sealed from the communication path 5 into the space 5a. The cooling water in the cooling water circulation path 6 is constantly circulated.
[0036]
Then, from gas cylinders 9 and 10 to SF ₆ Gas and C ₄ F ₈ Each gas is supplied into the etching chamber 2 a, high frequency power is applied to the coil 16, and high frequency power is applied to the base 3.
[0037]
SF supplied into the etching chamber 2a ₆ As shown in FIG. 2 (a), the gas flow rate is V _e2 To V _e1 In the range of a rectangular wave, and C ₄ F ₈ The gas flow rate is V, as shown in FIG. _d2 To V _d1 In the range of a rectangular wave, and SF ₆ Gas phase and C ₄ F ₈ Control is performed by the gas flow rate control means 21 so that the phases of the gases are opposite to each other.
[0038]
And SF ₆ Gas flow rate V _e1 And C ₄ F ₈ Gas flow rate V _d2 And flow rate ratio (ie, mixing volume ratio) V _e1 : V _d2 Is in the range of 100: 5-12, and SF ₆ Gas flow rate V _e2 And C ₄ F ₈ Gas flow rate V _d1 And flow rate ratio (ie, mixing volume ratio) V _e2 : V _d1 Is controlled by the gas flow rate control means 21 so as to be in the range of 2 to 5: 100.
[0039]
Further, the high frequency power applied to the coil 16 is W as shown in FIG. _c2 To W _c1 The high frequency power applied to the base 3 is changed to a rectangular wave shape in the range of W, as shown in FIG. _p2 To W _p1 The coil power control means 22 and the base power are changed so that the phase of the high frequency power applied to the coil 16 and the phase of the high frequency power applied to the base 3 are the same. It is controlled by the control means 23.
[0040]
SF supplied into the etching chamber 2a ₆ Gas and C ₄ F ₈ The gas becomes a plasma containing ions, electrons, F radicals, and the like within the varying magnetic field generated by the coil 16, and the plasma is maintained at a high density by the action of the varying magnetic field. The F radicals present in the plasma react chemically with Si to remove Si from the silicon substrate S, ie, to etch the silicon substrate S, and the ions are self-biased on the base 3 and the silicon substrate S. The electric potential is accelerated toward the base 3 and the silicon substrate S, and the silicon substrate S collides with the silicon substrate S to be etched. Thus, the surface of the silicon substrate S (etching ground) in the mask opening is etched by these F radicals and ions, and a groove or the like having a predetermined width and depth is formed.
[0041]
On the other hand, C ₄ F ₈ The gas is converted into a polymer by being turned into plasma, and is deposited on the wall surface and the bottom surface (etching ground) of the groove and the like, and functions to form a fluorocarbon film. This fluorocarbon film does not react with F radicals and acts as a protective film against F radicals, and side etching and undercut are prevented by this protective film.
[0042]
In this way, SF ₆ Gas and C ₄ F ₈ In the presence of plasma obtained by supplying gas into the etching chamber 2a at the same time, the opposite actions of etching by F radical and ion irradiation and formation of a protective film by polymerization proceed simultaneously on the wall surface and bottom surface of the groove or the like. . Specifically, at the bottom surface with a large amount of ion irradiation, the peeling of the polymer by ion irradiation acts more strongly than the deposition of the polymer, and the etching with F radicals and ions easily proceeds, while the wall surface with a small amount of ion irradiation. Then, the deposition of the polymer acts more strongly than the peeling of the polymer by ion irradiation, and the formation of the protective film is likely to proceed.
[0043]
In consideration of the above, in the present embodiment, SF ₆ Gas and C ₄ F ₈ As described above, the gas flow rate, the high frequency power applied to the coil 16 and the high frequency power applied to the base 3 are controlled as shown in FIG.
[0044]
Specifically, for the time zone indicated by e in FIG. ₆ Gas supply amount is V _e1 And more, C ₄ F ₈ Gas supply amount is V _d2 And reducing the high frequency power applied to the coil 16 to W _c1 The high frequency power applied to the base 3 is W _p1 It is high. SF ₆ Increase the gas supply amount, C ₄ F ₈ By reducing the amount of gas supply and increasing the high-frequency power applied to the coil 16, it is possible to generate an appropriate amount of F radicals and ions necessary for etching, while side etching and undercutting can be used to generate a polymer. The minimum amount that can be prevented can be suppressed. Further, by increasing the high frequency power applied to the base 3, the ion irradiation rate can be increased and the etching rate can be increased.
[0045]
As described above, for the etching ground (bottom surface) with a lot of ion irradiation, the peeling of the polymer by the ion irradiation acts more strongly than the deposition of the polymer, and the etching by the F radical or the ion proceeds while the ion irradiation. In the case of a wall with a small amount of deposit, the deposition of the polymer acts more strongly than the peeling of the polymer by ion irradiation, and the formation of the protective film proceeds, and the wall formed sequentially by etching is immediately covered with this protective film. The
[0046]
On the other hand, for the time zone indicated by d in FIG. ₆ Gas supply amount is V _e2 And less, C ₄ F ₈ Gas supply amount is V _d1 And the high frequency power applied to the coil 16 is W _c2 The high frequency power applied to the base 3 is W _p2 And lower. SF ₆ Reduce gas supply, C ₄ F ₈ By increasing the amount of gas supplied, more polymer can be generated to form the protective film, while generation of F radicals and ions is necessary to remove the polymer deposited on the etching ground. Can be kept to a minimum amount. In addition, by reducing the high frequency power applied to the base 3, the ion irradiation rate can be reduced to the extent necessary to peel off the polymer deposited on the etching ground, and the protection deposited on the wall surface. The film can be prevented from being peeled off by ion irradiation.
[0047]
As described above, with respect to the etching ground (bottom surface), etching is suppressed to such an extent that the deposited polymer is peeled off by ion irradiation. On the wall surface with less ion irradiation, more polymer is deposited and strong. A protective film is formed.
[0048]
Thus, by sequentially repeating the above steps e and d, the step of mainly etching and the step of mainly forming the protective film are alternately repeated and sequentially formed by etching. While the wall surface is immediately covered with the protective film, and the protective film is formed more firmly in the subsequent process, the above-mentioned side etching and undercut can be surely prevented, and thereby the inner A trench whose wall surface is vertical and whose unevenness is equal to or less than a predetermined reference value can be efficiently formed on the silicon substrate S.
[0049]
The SF for exhibiting such an action ₆ Gas flow rate V _e1 Is preferably in the range of 60 to 600 ml / min. ₄ F ₈ Gas flow rate V _d1 Is preferably in the range of 50 to 400 ml / min.
[0050]
Also, as described above, C ₄ F ₈ Gas flow rate V _d2 Is SF ₆ Gas flow rate V _e1 In the ratio V _d2 : V _e1 Is preferably in the range of 5 to 12: 100. V _d2 Is less than 5, C ₄ F ₈ The amount of gas is too small to effectively protect the wall formed by etching, while V _d2 Is over 12, C ₄ F ₈ This is because the amount of gas is too large, so that a protective film is easily formed on the etching ground, and the energy for performing the etching action is expended on the peeling of the protective film, thereby reducing the etching rate.
[0051]
SF ₆ Gas flow rate V _e2 Is C ₄ F ₈ Gas flow rate V _d1 In the ratio V _e2 : V _d1 The flow rate is preferably in the range of 2 to 5: 100. V _e2 If SF is less than 2, SF ₆ Since the amount of the gas is too small to sufficiently suppress the formation of the protective film on the etching ground, a sufficient etching rate cannot be obtained. _e2 If 5 exceeds 5, SF ₆ This is because the amount of gas is too large, and the wall surface is easily etched and the surface accuracy is deteriorated.
[0052]
In addition, the high frequency power W applied to the coil 16 _c1 Is preferably in the range of 800 to 3000 W, W _c2 Is preferably in the range of 600-2500W. Furthermore, the high frequency power W applied to the base 3 _p1 Is preferably in the range of 3-50W (more preferably 10-50W), W _p2 Is preferably in the range of 2 to 25 W (more preferably 5 to 25 W).
[0053]
Further, the execution time of the step e is preferably in the range of 3 to 45 seconds, and the execution time of the step d is preferably in the range of 3 to 30 seconds.
[0054]
Thus, according to this example, SF ₆ Gas and C ₄ F ₈ While using a mixed gas with a gas (fluorocarbon gas), the protective film forming gas is used in the etching progressing process by setting the mixed gas in the etching progressing process and the mixed gas in the protective film forming process to the above mixing ratios, respectively. In addition, the etching rate can be increased compared with an etching method that does not use an etching gas in the protective film formation step, and the wall surface formed by etching can be a smooth surface with high surface accuracy.
[0055]
By performing such highly accurate etching, the semiconductor integrated circuit can be highly integrated and densified, and a micromachine with high shape accuracy can be manufactured.
[0056]
【Example】
Hereinafter, more specific effects in the present invention will be described based on experimental examples.
[0057]
1. Experimental example 1
SF as etching gas ₆ Gas and C as protective film forming gas ₄ F ₈ High frequency power W applied to coil 16 using gas _c1 2200W, W _c2 Is 1500 W, and the high frequency power W applied to the base 3 _p1 40W, W _p2 Is set to 20W and SF of e process ₆ Gas flow rate V _e1 Is 450 ml / min and C in step d ₄ F ₈ Gas flow rate V _d1 Of 150 ml / min and SF in step d ₆ Gas flow rate V _e2 Is changed to 0 ml / min, 3 ml / min, 4.5 ml / min, 7.5 ml / min, 15 ml / min, and C in step e. ₄ F ₈ Gas flow rate V _d2 The silicon substrate was etched under various conditions of 0 ml / min, 22.5 ml / min, 31.5 ml / min, 54 ml / min, 90 ml / min, and 135 ml / min. A hole 31 as shown in FIG.
[0058]
In addition, the processing time of e process was set to 8.5 seconds, the processing time of d process was set to 3 seconds, and this e process and d process were repeated for 15 minutes. The pressure in the etching chamber 2 was 4.0 Pa in the e process and 1.9 Pa in the d process.
[0059]
Then, the etching rate under the above etching conditions, the surface accuracy (unevenness) ρ (nm) of the formed hole wall surface 32, and the angle θ (°) of the wall surface 32 with respect to the groove bottom surface were measured. The results are shown in FIGS. FIG. 4 is a table showing the measurement results of the etching rate (μm / min) under the above etching conditions, and FIG. 5 is a graph thereof. FIG. 6 is a table showing the measurement results of the surface accuracy (unevenness) ρ (nm), and FIG. 7 is a graph thereof. FIG. 8 is a table showing measurement results of the angle θ (°), and FIG. 9 is a graph thereof.
[0060]
In FIGS. 4, 6, and 8, SF is used. ₆ Gas flow rate V _e2 Is C ₄ F ₈ Gas flow rate V _d1 This is expressed as a flow rate (volume) ratio when (150 ml / min) is 100, and C ₄ F ₈ Gas flow rate V _d2 Similarly, SF ₆ Gas flow rate V _e1 This is expressed as a flow rate (volume) ratio when (450 ml / min) is 100.
[0061]
As shown in FIG. 4 to FIG. ₆ When no gas is used (when A = 0), C in the e process ₄ F ₈ Gas flow rate V _d2 The surface accuracy (irregularity) ρ (nm) and the angle θ (°) are improved as the number is increased, but the etching rate tends to decrease. ₄ F ₈ When gas is not used, SF in d process ₆ Gas flow rate V _e2 It can be seen that the etching rate increases as the number increases, but the surface accuracy (unevenness) ρ (nm) and the angle θ (°) tend to deteriorate.
[0062]
And from this result, SF in d process ₆ Gas flow rate V _e2 And C in step e ₄ F ₈ Gas flow rate V _d2 It is expected that the etching rate, the surface accuracy (unevenness) ρ (nm), and the angle θ (°) can each be made favorable by adjusting the amount to be an appropriate amount. To SF as shown in FIG. ₆ Gas flow rate V _e2 C ₄ F ₈ Gas flow rate V _d1 The flow rate ratio to C is in the range of 2 to 5, and C ₄ F ₈ Gas flow rate V _d2 SF ₆ Gas flow rate V _e1 When the flow ratio with respect to is in the range of 5 to 12, ₄ F ₈ SF without using gas and d process ₆ It has been found that the etching rate is faster and the surface accuracy (unevenness) ρ (nm) and angle θ (°) can be improved compared to the case where no gas is used (that is, when A = 0 and B = 0). .
[0063]
Note that the higher the etching rate, the better. However, in this example, as described above, C in the e step. ₄ F ₈ SF without using gas and d process ₆ Compared with the case where no gas is used (that is, when A = 0 and B = 0), an etching rate that is comparable or higher is determined as a preferable rate. Moreover, it is preferable that the surface accuracy (unevenness) ρ (nm) is small, but it is C in the e process. ₄ F ₈ SF without using gas and d process ₆ Compared with the case where no gas is used (that is, when A = 0 and B = 0), the surface accuracy that is approximately equal to or less than that is determined as a preferable accuracy. Furthermore, the angle θ (°) is more preferably close to 90 °, but a preferable angle is 91 ° or less.
[0064]
2. Experimental example 2
SF as etching gas ₆ Gas and C as protective film forming gas ₄ F ₈ High frequency power W applied to coil 16 using gas _c1 900W, W _c2 Is 800 W, and the high frequency power W applied to the base 3 _p1 25W, W _p2 Is set to 5W and SF of e process ₆ Gas flow rate V _e1 Is 200 ml / min, and C in step d ₄ F ₈ Gas flow rate V _d1 Of 60 ml / min and SF in step d ₆ Gas flow rate V _e2 Is changed to 0 ml / min, 1.2 ml / min, 1.8 ml / min, 3 ml / min, 6 ml / min, and C in step e. ₄ F ₈ Gas flow rate V _d2 Is etched under various conditions of 0 ml / min, 10 ml / min, 14 ml / min, 24 ml / min, and 40 ml / min to form a hole 31 as shown in FIG. 3 on the silicon substrate. did.
[0065]
In addition, the processing time of e process was 15 seconds, the processing time of d process was 7 seconds, and this e process and d process were repeated for 30 minutes. The pressure in the etching chamber 2 was 2.5 Pa in the e process and 0.8 Pa in the d process.
[0066]
Then, under the above etching conditions, the etching rate, the surface accuracy (unevenness) ρ (nm) of the formed hole wall surface 32, and the angle θ (°) of the wall surface 32 with respect to the groove bottom surface were measured. The results are shown in FIGS. FIG. 10 is a table showing the measurement results of the etching rate (μm / min) under the above etching conditions, and FIG. 11 is a graph thereof. FIG. 12 is a table showing measurement results of the surface accuracy (unevenness) ρ (nm), and FIG. 13 is a graph thereof. FIG. 14 is a table showing measurement results of the angle θ (°), and FIG. 15 is a graph thereof.
[0067]
In FIGS. 10, 12, and 14, SF is used. ₆ Gas flow rate V _e2 Is C ₄ F ₈ Gas flow rate V _d1 This is expressed as a flow rate ratio when (60 ml / min) is 100, and C ₄ F ₈ Gas flow rate V _d2 Similarly, SF ₆ Gas flow rate V _e1 This is expressed as a flow rate ratio when (200 ml / min) is 100.
[0068]
As shown in FIGS. 10 to 15, also in this experimental example, SF is used in the d step. ₆ When no gas is used (when A = 0), C in the e process ₄ F ₈ Gas flow rate V _d2 The surface accuracy (irregularity) ρ (nm) and the angle θ (°) are improved as the number is increased, but the etching rate tends to decrease. ₄ F ₈ When gas is not used, SF in d process ₆ Gas flow rate V _e2 As the number increases, the etching rate increases, but on the other hand, the surface accuracy (unevenness) ρ (nm) and the angle θ (°) tend to deteriorate. ₆ Gas flow rate V _e2 And C in step e ₄ F ₈ Gas flow rate V _d2 It can be seen that the etching rate, the surface accuracy (unevenness) ρ (nm), and the angle θ (°) can each be made favorable by adjusting the amount to a suitable amount.
[0069]
Also in this experimental example, as shown in FIGS. ₆ Gas flow rate V _e2 C ₄ F ₈ Gas flow rate V _d1 The flow rate ratio to C is in the range of 2 to 5, and C ₄ F ₈ Gas flow rate V _d2 SF ₆ Gas flow rate V _e1 It was found that the etching rate, surface accuracy (unevenness) ρ (nm), and angle θ (°) can all be improved when the flow rate ratio with respect to is in the range of 5 to 12. The preferable ranges of the etching rate, surface accuracy (unevenness) ρ (nm), and angle θ (°) depend on the same criteria as those in the experimental example 1.
[0070]
In Experimental Example 2, the high frequency power W applied to the coil 16 as compared with Experimental Example 1 _c1 And W _c2 The high frequency power W applied to the base 3 _p1 And W _p2 And lower the SF accordingly. ₆ Gas flow rate V _e1 And C ₄ F ₈ Gas flow rate V _d1 The experiment was performed under the condition of reducing the frequency of the high frequency power W applied to the coil 16 as can be seen from Experimental Examples 1 and 2. _c1 , W _c2 And high frequency power W applied to the base 3 _p1 , W _p2 SF regardless of the size of the ₆ Gas flow rate V _e1 And C ₄ F ₈ Gas flow rate V _d1 SF with or without much ₆ Gas flow rate V _e2 C ₄ F ₈ Gas flow rate V _d1 The flow rate ratio to C is in the range of 2 to 5, and C ₄ F ₈ Gas flow rate V _d2 SF ₆ Gas flow rate V _e1 It was found that the etching rate, the surface accuracy (unevenness) ρ (nm), and the angle θ (°) can all be improved when the flow ratio with respect to is in the range of 5 to 12.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a schematic configuration of an etching apparatus according to an embodiment in a partial block diagram.
FIG. 2 SF ₆ Gas and C ₄ F ₈ It is a timing chart which shows the flow state of gas, and the control state of the high frequency electric power applied to a coil and a base.
FIG. 3 is an explanatory diagram for explaining an evaluation method in an experimental example.
4 is a table showing measurement results of etching rate in Experimental Example 1. FIG.
5 is a graph showing measurement results of etching rate in Experimental Example 1. FIG.
6 is a table showing measurement results of surface accuracy ρ in Experimental Example 1. FIG.
7 is a graph showing measurement results of surface accuracy ρ in Experimental Example 1. FIG.
8 is a table showing measurement results of angle θ in Experimental Example 1. FIG.
9 is a graph showing measurement results of angle θ in Experimental Example 1. FIG.
10 is a table showing measurement results of etching rate in Experimental Example 2. FIG.
11 is a graph showing measurement results of etching rate in Experimental Example 2. FIG.
12 is a table showing measurement results of surface accuracy ρ in Experimental Example 2. FIG.
13 is a graph showing measurement results of surface accuracy ρ in Experimental Example 2. FIG.
14 is a table showing measurement results of an angle θ in Experimental Example 2. FIG.
15 is a graph showing a measurement result of an angle θ in Experimental Example 2. FIG.
[Explanation of symbols]
S silicon substrate
1 Etching equipment
2 Etching chamber
2a Etching chamber
3 base
7 Gas supply section
8 Gas supply pipe
9,10 Gas cylinder
11,12 Mass flow controller
13 Pressure reducing part
14 Exhaust pipe
15 Plasma generator
16 coils
17, 18 High frequency power supply
20 Control device
21 Gas flow control means
22 Coil power control means
23 Base power control means

Claims (6)

A mask forming step of forming an etching mask on the surface of the silicon substrate, and an etching step of dry-etching the surface of the silicon substrate from an opening of the etching mask using an etching gas that has been made plasma by high-frequency power to form a predetermined structure surface And sequentially etching the silicon substrate,
The etching step,
While constantly applying power to the silicon substrate to give a bias potential,
Using a mixed gas of SF ₆ gas as an etching gas and a fluorocarbon gas as a protective film forming gas, to advance the dry etching mainly at an etching ground;
Similarly, in the etching method in which a mixed gas of SF ₆ gas and fluorocarbon gas is used and the step of forming a protective film mainly on the structure surface perpendicular to the etching ground is sequentially repeated.
The mixed gas in the dry etching progress step is a mixture of 5 to 12 volumes of fluorocarbon gas with respect to 100 volumes of SF ₆ gas,
An etching method for a silicon substrate, wherein the mixed gas in the protective film forming step is a mixture of 2 to 5 volumes of SF ₆ gas with respect to 100 volumes of fluorocarbon gas. 2. The method of etching a silicon substrate according to claim 1, wherein the power applied to the silicon substrate is increased in the dry etching progress step and is decreased in the protective film forming step. 3. The method of etching a silicon substrate according to claim 1, wherein high-frequency power for generating plasma in the etching step is increased in the dry etching progress step and is decreased in the protective film forming step. . An etching chamber for storing a silicon substrate to be etched;
A base disposed at a lower position in the etching chamber and on which the silicon substrate is placed;
Etching gas supply means for supplying SF ₆ gas as an etching gas into the etching chamber;
Protective film forming gas supply means for supplying a fluorocarbon gas as a protective film forming gas into the etching chamber;
Decompression means for decompressing the inside of the etching chamber;
Plasma comprising a coil disposed on the outer periphery of the etching chamber so as to face the coil, and applying high frequency power to the coil to convert the SF ₆ gas and fluorocarbon gas supplied into the etching chamber into plasma Generating means;
Base power application means for applying high frequency power to the base;
Gas flow rate control means for controlling the flow rates of the SF ₆ gas and the fluorocarbon gas supplied into the etching chamber by the etching gas supply means and the protective film forming gas supply means;
Coil power control means for controlling power applied to the coil of the plasma generating means;
A base power control means for controlling the power applied to the base by the base power application means,
The gas flow rate control means supplies the SF ₆ gas and the fluorocarbon gas continuously into the etching chamber while changing the supply amounts periodically, and controls the supply amounts so that the phases of both are reversed. controlled, further, the SF ₆ fluorocarbon gas 5-12 volume supplied to the SF ₆ gas 100 capacity when a large amount supply of gas, the 2 SF ₆ gas to fluorocarbon gas 100 capacity when a large amount supply of fluorocarbon gas A silicon substrate etching apparatus characterized by being configured to supply up to 5 volumes. The base power control means is configured to increase the power applied to the base when the SF ₆ gas is supplied in a large amount and to reduce the power when the fluorocarbon gas is supplied in a large amount. Item 5. A silicon substrate etching apparatus according to Item 4. 5. The coil power control means is configured to increase the power applied to the coil when a large amount of the SF ₆ gas is supplied and to decrease when the SF ₆ gas is supplied in a large amount. Or the silicon substrate etching apparatus according to 5.

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